Frequent infection with human papillomavirus (HPV) in the oral cavity has been noted in HIV immunocompromised children and adults. HIV-infected individuals are more susceptible to infection with multiple HPV subtypes, including types 16 and 18. These "high risk" HPVs that are closely associated with development of malignant oral cancer: the viral DNA is frequently found in oral cancer cells and tissue. Moreover, transfection of normal human oral keratinocyte (NHOK) cells with cloned "high risk" HPV genome immortalizes these cells, which can convert to fully transformed cells when exposed to chemical carcinogens. Since (1) the same chemical carcinogens cannot transform NHOK cells and (2) the loss of genomic integrity is the hallmark of neoplastic cells, "high risk" HPV must play a critical role in the malignant transformation of NHOK cells by disrupting cells' ability to maintain genomic integrity. Genomic integrity is maintained by constant repair of DNA damage; thus, disturbance of DNA repair results in mutations, which ultimately induces malignant transformation of cells. The central hypothesis of the project is that infection of NHOK cells with "high risk" HPV oncogenes disrupts DNA repair; and that inhibition of HPV oncogene expression allows pre-neoplastic human oral epithelial cells expressing high risk" HPV oncogenes to regain their DNA repair activities and genomic integrity. To test this hypothesis, the applicants propose the following specific aims: (1) to determine the basal and genotoxic agent-induced DNA repair activities of NHOK cells, HOK cells transfected with the HPV-16 genome, and pre-neoplastic oral epithelial cells (derived from lesion biopsies) expressing "high risk" HPV; (2) to investigate the effects of HPV-16 oncogenes on basal and genotoxic agent-induced DNA repair activities of NHOK cells; and (3) to study the effect of "high risk" HPV ribozymes on DNA repair activities and mutation frequency (and rate) of hypoxanthine phosphoribosyl transferase (hprt) gene of pre-neoplastic and neoplastic human oral epithelial cells (expressing "high risk" HPV) derived from lesion biopsies. The applicants expect to answer the following questions: Does "high risk" HPV disrupt the repair of DNA damage in NHOK cells? If so, which DNA repair process is impaired? Are viral oncogenes responsible for such disruption? If so, is the inactivation of p53 or pRB by HPV oncogenes solely responsible for the disruption? Do pre-neoplastic or neoplastic cells (expressing "high risk" HPV) derived from human oral lesion biopsies have the same spectrum of DNA repair defects as NHOK cells transfected with "high risk" HPV genome? Does the disruption of viral oncogene transcripts restore the DNA repair activites and genomic integrity of HPV-immortalized HOK cells, pre-neoplastic and neoplastic human oral epithelial cells (from lesion biopsies) expressing "high risk" HPV oncogenes?